Background coloration inhibition in diazosulfonate photoreproduction

ABSTRACT

INCLUSION OF A NEUTRAL SALT OF AN AROMATIC SULFINIC ACID IN A REVERSAL DIAZOSULFONATE PHOTOSENSITIVE COMPOSITION PREVENTS BACKGROUND COLORATION.

United States Patent O 3,623,875 BACKGROUND COLORATION INHIBITION IN DIAZOSULFONATE PHOTOREPRODUCTION Robert Charles Desjarlais, South Hadley Falls, Mass., assignor to The Plastic Coating Corporation, South Hadley, Mass. No Drawing. Filed Nov. 28, 1969, Ser. No. 880,902 Int. Cl. G03c 1/56, 1/60 US. Cl. 96-91 6 Claims ABSTRACT OF THE DISCLOSURE Inclusion of a neutral salt of an aromatic sulfinic acid in a reversal diazosulfonate photosensitive composition prevents background coloration.

BACKGROUND OF THE INVENTION Field of the invention The invention described herein was made under a contract with the United States Air Force. The present invention relates to photosensitive diazosulfonate formulations and to diazo photographic reproduction materials made therefrom.

Description of the prior art In US. patent application Ser. No. 464,447, new U.S. Pat. No. 3,479,183 issued Nov. 18, 1969, there is disclosed and claimed a negative-working or reversal diazo photographic reproduction (photoreproduction) material made from a formulation comprising a para-amino benzene diazosulfonate, a coupler (i.e., a color former) therefor and a substantially non-volatile amine. This formula tion is applied as a discrete layer upon the surface of a support. The resulting light-sensitive material is useful for photographically reproducing images contained in master transparencies, such as microfilm, engineering drawings, and aerial photographs, through the action of light on the diazo formulation.

The image-producing process described in the aforementioned patent application comprises the steps of imagewise exposing the diazo imaging-material to actinic illumination (blue-violet and ultraviolet light) to convert the diazosulfonate to an active diazonium compound which couples with a coupling component to provide a dyeimage in the light-struck areas; acidifying the discrete layer with acid vapor; and light clearing the unreacted diazosulfonate by exposing it overall to actinic illumination, thereby forming colorless decomposition products of the diazosulfonate to produce a stable, fixed, dye-image against a clear background. The mechanism of the negative-working diazosulfonate process during the light-clearing step may be represented in the following manner:

ArNfHSOr 11 l ArOH mso, N21

wherein Ar is a para-amino benzene radical and M is an alkali metal.

Organic polyhydroxy compounds such as the glycols, mannitols, sorbitols, and the like are incorporated in the reversal diazosulfonate imaging formulation of the above-mentioned patent application to serve as humectants or plasticizers. Humectants exert a stabilizing effect on the water content of the layer of photoreproduction material. Their inclusion helps to maintain the adhesion of the photosensitive coating to the base or support material. Humectants also enhance the coupling reaction because the proper water content ensures mobility of the reactive chamicals. These compounds are so effective in ice favoring the coupling reaction, however, that azo dye formation can also occur during the clearing operation, thereby producing an undesirable background coloration. In the same manner, loss of brightness or clarity in the background can occur during aging of the fixed print as it is exposed to ordinary room light.

Accordingly, it is an object of the present invention to prevent azo dye formation during the clearing step in the process of forming an image in reversal diazosulfonate photoreproduction material.

Another object of the invention is to provide improved retention of brightness in the background areas of the fixed image as it ages and is exposed to light.

SUMMARY OF THE INVENTION In accordance with the present invention the incorporation of a neutral salt of an aromatic sulfinic acid into the above-described diazosulfonate formulation prevents the diazonium compound derived from the diazosulfonate from coupling during and after the clearing step.

Either alkali metal salts or amine salts of the aromatic sulfinic acid can be employed in the formulations of the present invention.

While the present inventor does not wish to be bound to any particular theory, he suspects that the following reactions occur during the clearing operation:

ArSO M RCOOH ArSO H RCOOM hv ArSO H 1/20 ArS0 H wherein Ar is an aryl radical, M is an alkali metal or amine group, and R is hydrogen, an aryl or alkyl radical.

It is postulated that the aromatic sulfinic acid salt (sulfinate) is converted by the acid during the clearing step to free sulfinic acid, which is then light-oxidized to sulfonic acid. Since sulfonic acid is comparable in acidic strength to sulfuric acid, the presence of even a small amount prevents coupling during the clearing step. Accordingly, no narrow range of concentrations of the sulfinate can be described as critical, and provided that more than trace amounts are used, satisfactory results are obtained through the use of a wide range of concentrations, the preferred being a concentration equal to the molar concentration of the diazosulfonate compound. The sulfinate must be approximately neutral in an aqueous medium so that it does not significantly lower the pH of the photoreproduction material, which must be above pH 5 during the exposure step. If not neutral, the salt should preferably be slightly alkaline and hence compatible with the alkalinity of the medium prior to exposure.

Many alkali metal salts of sulfinic acid, e.g. sodium paratoluene sulfinate, are commercially available reagents, and hence their preparation is not necessary to the practice of this invention. Salts not commercially available can be readily prepared by techniques well known in the art. The preparation of sulfinic acids is described in such standard works as Feiser and Feiser, Organic Chemistry 2nd edition 1950, page 631 and Wagner and Zook, Synthetic Organic Chemistry 1953, page 807. Sulfinic acids can be prepared by the reduction of a sulfonyl chloride or by the Grignard reaction. The sulfinates can readily be derived from the free sulfinic acids by reacting them in water with an alkali metal hydroxide and salting out the sulfinate.

The amine salts can be prepared by combining the free sulfinic acid and an amine in ether, from which the amine sulfinate precipitates. Instead of isolating the amine salt of the sulfinic acid, however, it is preferred to simply add the appropriate amounts of the free sulfinic acid and the amine to the light-sensitive coating formulation and allowing the amine salt to form in situ.

3 DESCRIPTION OF PREFERRED EMBODIMENTS Example I A solution comprising: Half-second acetate" (a low-viscosity cellulose diacctate)1 6 g. Methanol30 cc. Acetone-70 cc. Polypropylene glycol (average molecular weight 400) 3 cc. Ortho-sulfobenzaldehyde, sodium salt-1.44 g. 2 hydroxy 3 naphthoic acid ortho anisidide (2- hydroxy-3-naphthoic acid, 2'-methoxy-anilide)1.29 g.

l-hydroxy-Z-naphthoic acid piperidide0.44l g.

N-isopropyl, N-cyclohexyl aminel.28 g. 4-(N-ethyl, N-benzylamino) benzene diazosulfonate, so-

dium salt1.75 g. Sodium para-toluene sulfinate-1.09 g.

This solution was coated, by means of a No. 36 Mayer bar, onto a sheet of polyester which was provided with a suitable bonding layer and dried. The resulting film was then exposed to actinic light under a partially opaque master to give a black image in the unprtectedi.e. light struck-areas. The film was then fixed and the background areas cleared by acidifying with formic acid vapors and re-exposing the entire film to actinic light. The amount of background coloration which was observed with the above formulation was measured with a photoelectric brightness meter, using White Cararra glass as the brightness standard. This film had a brightness in the clear areas of 65.5. By comparison, a control composition which did not contain the sodium para-toluene sulfinate had a brightness of 61.0. After one weeks (seven days) exposure to normal room light, the print formed from the composition containing the sodium para-toluene sulfinate had a brightness in the clear areas of 59.0, whereas the control, after the same exposure, had a brightness of 495.

Example II In the formula of Example I, a combination of 0.876 g. of 4-(N-ethyl, N-benzylamino)benzene diazosulfonate, sodium salt, and 0.826 g. of 4-(N-2,6 dimethyl morpholino)-benzene diazosulfonate, sodium salt, was substituted for the 1.75 g. of the 4-(N-ethyl, N-benzylamino)-benzene diazosulfonate, sodium salt.

When coated, printed and cleared as in Example I, the film had a brightness in the cleared areas of 67.0. By comparison a control composition which did not contain the sodium para-toluene sulfinate had a brightness of 59.5.

After one weeks exposure to normal room light, the print formed from the composition containing the sodium para-toluene sulfinate had a brightness in the clear areas of 54.0, whereas the control, after the same exposure, had a brightness of 48.5.

Example III In the formula of Example I, in place of the sodium paratoluene sulfinate the N-isopropyl, N-cyclohexyl amine salt of paratoluene sulfinic acid was formed in situ by adding 0.80 g. of para-toluene sulfinic acid and an additional 0.72 g. of N-isopropyl, N-cyclohexyl amine to the formula.

When coated, printed and cleared as in Example I, the film had a brightness in the clear areas of 66.0. A control composition which did not contain the paratoluene sulfinic acid amine salt, produced a brightness of 61.0. After one weeks exposure to normal room light, the sample print formed from the composition containing the amine salt had a brightness in the clear areas of 52.5, and the control print, after the same exposure, had a brightness of 52.5.

Example IV In the formula of Example I, 1.00 g. of lithium paratoluene sulfinate was substituted for sodium para-toluene sulfinate.

When coated, printed and cleared as in Example I, the film had a brightness in the clear areas of 64.5. A control composition which did not contain lithium paratoluene sulfinate, produced a brightness of 61.0. After one weeks exposure to normal room light, the sample print had a background brightness of 57.0, whereas the control, after the same exposure, had a brightness of 52.5.

Example V A solution comprising:

Half-second acetate16 g.

Methanol-30 cc.

Acetone-70 cc.

Polypropylene glycol (average molecular weight 400) Ortho-sulfobenzaldehyde, sodium salt1.44 g.

2-hydroxy-3-naphthoyl-o-anisidide-l.05 g.

1-hydroxy-2-naphthoyl piperidide.645 g.

N-isopropyl, N-cyclohexyl amine-.5 g.

4-(N-ethyl, N-benzylamino)-benzene diazosulfonate sodium salt1.75 g.

Hydroxypropyl sorbitol2.6 g.

Sodium para-toluene sulfinate-1.09 g.

This solution was coated, by means of a No. 36 Mayer bar, onto a sheet of ethyl cellulose-treated, baryta-sized paper and dried. The paper was then exposed to actinic light under a partially opaque master to give a black image in the unprotectedi.e., light struck-areas. The print was then fixed and the background areas cleared by acidifying with formic acid vapors and re-exposing the entire sheet to actinic light. This print had a background density (D value of 0.14 as measured by a photoelectric densitometer calibrated for visual density according to the ASA specification for reflectance density, pH 2. 17-1958. In the printed areas, by comparison, the image had a maximum density (D of 2.06. Little or no color in the background areas of a print with these D and D values can be discerned by an examination with the unaided eye. By comparison, a control print which did not include the sodium para-toluene sulfinate had a background density (D of 0.21. After one weeks exposure to normal room light, the rint formed from the composition containing sodium paratoluene sulfinate had a D in the clear areas (background) of 0.23 whereas the control, after the same exposure, had a D of 0.30.

Example VI A solution comprising:

Half-second acetate16 g.

Methanol30 cc.

Acetone70 cc.

Polypropylene glycol (average molecular weight 400) Ortho-sulfobenzaldehyde sodium salt-1.44 g.

2-hydroxy-3-napthoyl-o-anisididel.29 g.

1-hydroxy-2-naphthoyl piperidide0.441 g.

N-isopropyl, N-cyclohexylamine1.28 g.

4-(N-ethyl, N-benzylamino)-benzene diazosulfonate sodium salt-1.75 g.

Sodium benzene sulfinate-0.83 g.

This solution was coated, printed and cleared as in Example V. This print had a background density (D value of 0.14. By comparison, a control print which did not include the sodium benzene sulfinate had a background density (D of 0.22. After one weeks exposure to normal room light, the print formed from the composition containing sodium benzene sulfinate had a background D of 0.15, whereas the control print, after the same exposure, had a D of 0.26.

Other aromatic sulfinic acids which are commercially available or which can readily be prepared from commercially available compounds include: 4-acetamido benzene sulfinic acid, S-acetamido benzene sulfinic acid, para-methoxy benzene sulfinic acid, 4-N,N-dimethylamino benzene sulfinic acid, ortho-methoxy benzene sulfinic acid, para-bromobenzene sulfinic acid, para-chlorobenzene sulfinic acid, para-fiuorobenzene sulfinic acid, alpha-naphthalene sulfinic acid, ortho-toluence sulfinic acid, and 2- dibenzofuran sulfinic acid. These acids can be converted to the sulfinates by the methods described above and used in the same manner as the specific sulfinates illustrated in the examples above.

While the invention has been described with reference to preferred embodiments thereof, it is understood that various other changes and modifications thereof will occur to a person of ordinary skill in the art without departing from the spirit and scope of the invention, as defined by the appended claims.

What is claimed is:

1. In a photosensitive diazo formulation comprising a para-amino benzene diazosulfonate, an azo coupling component and a substantially non-volatile amine, the improvement which comprises the inclusion of an alkali metal or amine salt of an aromatic sulfinic acid.

2. The formulation according to claim 1, wherein the salt is an alkali metal salt of an aromatic sulfinic acid.

3. The formulation according to claim 1, wherein the salt is an amine salt of an aromatic sulfinic acid.

4. A reversal diazo photoreproduction material which comprises a support and a photosensitive layer coated on a surface of the support, said layer comprising the formulation according to claim 1.

5. The material according to claim 4, wherein the salt is an alkali metal salt of an aromatic sulfinic acid.

6. The material according to claim 4, wherein the salt is an amine salt of an aromatic sulfinic acid.

References Cited UNITED STATES PATENTS 2,854,338 9/1958 Herrick et a1. 9649 X 3,479,183 11/1969 Habib et a1. 9649 OTHER REFERENCES Dinaburg, M.: Photosensitive Diazo Compounds, 1964, pp. 5152 and 93.

'Fieser et al.: Organic Chemistry, 3rd ed., 1956, pp. 593-594.

NORMAN G. TORCHIN, Primary Examiner C. L. BOWERS, JR., Assistant Examiner US. Cl. X.R. 9649 

